Discharging zakaat for previous years

Q: Until recently I thought I did not have to give zakat because I was under the assumption there was only one nisab, the nisab for gold, and I have never owned more than the nisab for gold. However now I am aware that there is a nisab for silver, and that this should be used when calculating zakat. Since I haven’t paid zakat until now, I would like to start calculating my zakat for the previous years as well as for this year however I have some questions as I haven’t calculated zakat before:

1) Do I estimate how much zakatable assets I have at the END of each zakat year and then pay 2.5% of that in zakat?

2) The nisab value constantly changes, for example at the moment the nisab for is around £294, but previous years it was different. So when determining if I own above the nisab in previous years and am therefore eligible for paying zakat, since I don’t know what the nisab was in those years should I use the current nisab when calculating for previous years?

3) Since I did not know I had to pay zakat, I also have not taken part in qurbani (udhiya). How should I go about calculating how much I owe for this?

4) Can I pay my zakat through an islamic charitable organisation, such as MuslimAid, IslamicRelief, etc?

Forgive me for the long question, but I want to make sure i’m paying zakat correctly, especially as I had been ignorant of it for many years. May Allah subhanahu wa ta’ala make it easy for us to fulfil our religious obligations.

A:

1. Yes, each lunar year.

2. It is not difficult to find out the nisaab of the previous years. The people that deal with gold and silver, they generally have the records for the past years as well.

3. First work out whether you were required to make qurbani and thereafter give sadaqah for each year. The sadaqah will have to be equivalent to a qurbani animal valued at the present rate.

4. If you are hundred percent sure that they know about the masaa’il and they will use it in the correct avenues then it is permissible.